Bias Layer: Add support for regularizer and constraint

[saisua]

Small patch to add the bias_regularizer and bias_constraint. It is needed to be like other layers in TF2.0. They are initialized as None based on current master.

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[saisua]

I just did that. Thank you for your quick response. As a side note, I have seen that there is a file called something like "bias layer test". I have not touched it but feel free to ask for anything.

[sguada]

Please add 2 new test to make sure the new arguments work as expected.

[tfboyd]

This has been about 1.5 years. I am making this closed. We can always reopen. I am merging PRs where with my knowledge can get the merged. This one is too big for me to handle unfortunately. Sometimes things rot on the vine; sad and a reality.

Thank you for the effort and sorry this did not make it to the finish.